The present invention relates to a digital mobile communication system and, more particularly, to a radio frame synchronization system for controlling synchronization of a radio frame transmitted from a radio base station to a mobile station.
In a mobile communication system using digital signals, a technique of matching the phases of signals transmitted from radio base stations is indispensable to effective use of radio frequencies and incessant switching of radio channels.
As a first example of such a conventional technique, a technique like the one disclosed in Japanese Patent Laid-Open No. 58-131842 is available. According to this technique, a reference signal transmitted from a satellite is received by each radio base station, and a signal from a wire line is transmitted in synchronism with this reference signal.
As a second example, a technique like the one disclosed in Japanese Patent Laid-Open No. 2-26135 is available. According to this technique, a radio base station for transmitting a phase reference signal is installed, and the remaining radio base stations receive a phase reference signal from this radio base station. A signal from a wire line is then transmitted in synchronism with this phase reference signal.
In the first example, however, each radio base station must have a dedicated receiver for receiving a reference signal from the satellite. For this reason, each radio base station cannot be reduced in size. In the second example, a special radio base station for transmitting a phase reference signal is required.